1. Field of the Invention
The present invention relates to an image binarization method and a binary image creation method that are directly required for television images, in particular, an image binarization method and a binary image creation method wherein thresholds in binarization are not fixed, but set in accordance with changes in luminance, and real-time images can be obtained.
The more vivid such a binary image, the easier the automated inspection of imaged objects and shape judgement including character detection, and this is efficient.
2. Description of the Related Art
In Japanese Unexamined Patent Publication No. H01-267425, an image processing method and device for imaging systems are disclosed, wherein video signals are binarized at a desired level and stored in a plurality of frame (image) memories, and then logical processing between pixels is carried out between frame memories, and binarization is carried out again.
In Japanese Unexamined Patent Publication No. H04-255078, an image processing device is disclosed, wherein, with respect to a change in luminance distribution of a part of an image, a binarization reference value is determined by means of a histogram of the abovementioned part.
Likewise, in Japanese Unexamined Patent Publication No. H04-372073, a threshold determination method for binarization is disclosed wherein a threshold is determined by means of each histogram of the contrast intensity and opposing intensity.
In Japanese unexamined Patent Publication No. H05-180781, a surface defective inspection method and device are disclosed wherein two images are obtained, and smoothing is applied to one image and an offset value is evenly added to determine a threshold, and the other image is binarized.
In Japanese Unexamined Patent Publication No. H04-175985, a number of thresholds, which start from the central value of the density level and are successively changed to higher and lower values are set, and binarized, and the thresholds at which the detected number of characters and the known number of characters become equal to each other are selected, and then a desired threshold is set.
It has been conventionally demanded that multi-digitized luminance data obtained by digitally converting video signals from an imaging device for each pixel on each horizontal scanning line is used, and converted into binary data in a form with the highest fidelity for the data to create an image.
Threshold setting for binarization and binarizing conversion are executed after video signals are collected and stored in image memories as digital values in all the abovementioned conventional examples, that is, the setting and processing are executed as post-processing during image processing.